1. Field of the Invention
The invention relates to portable voice communications systems for establishing direct voice contact between individuals wearing air breathing equipment with face masks.
2. Background of the Invention
Firemen and other emergency personnel, as well as workers in certain industries, are often required to wear protective air breathing apparatus or masks to avoid the toxic effects of noxious gases, smoke, chemical fumes, vapors and airborne particulate matter. The mask or other breathing apparatus covering the mouth and nose severely attenuates unaided speech and makes vocal communication with other individuals most difficult, if not impossible, particularly where an airtight seal must be maintained.
In the past, systems have been devised to place small conventional microphones within the mask or other breathing apparatus to generate an electrical signal that can be amplified to drive a small speaker unit worn by the individual. However, such prior systems have not been satisfactory for several reasons. To begin with, the breathing apparatus or mask provides an irregularly shaped confined space that distorts the wearer's voice patterns with unpredictable reverberation, resonance and reflection effects that depend upon the shape of the mask relative to the covered area of the user's face. As a consequence, the signal produced by the microphone and amplified to drive the speaker produces a garbled speech pattern that lacks clarity and is frequently inaudible to the untrained listener. In addition, wires connecting the microphone inside the amplifier and loudspeaker unit must pass through the mask which can inherently compromise the integrity of the airtight seal required pursuant to various safety regulations, and with extended or vigorous use may actually be pulled loose.
These problems are further aggravated by the limitations of the sound amplification and speaker units which, with their self contained power sources, must be relatively small and lightweight so that users can carry them without unduly hampering their movements or interferring with their ability to handle tools and other emergency equipment. Accordingly, the quality and volume of the speech sound reproduced by the speaker is often less than adequate, especially in industrial and emergency environments where background noise is high. The natural tendency of most people to talk louder or to shout to make themselves understood only increases sound distortions due to reverberation, resonance and reflection within the mask and also often overloads the low power amplifier beyond its undistorted dynamic range limits to introduce further distortion.
Throat microphones have long been used previously, especially by crews in unpressurized aircraft for voice communication at higher altitudes where oxygen masks are worn. Although this avoids the problems due to placing a microphone within the mask, throat microphone systems are subject to other difficulties that have impaired their successful use in portable voice communication systems. Generally throat microphones primarily respond to the lower frequency components of normal speech. However with conventional amplifying methods severe distortion due to the sizable phase shift differences between different low frequency components occur. Thus untrained listeners often have difficulty understanding speech reproduced from throat microphone systems and thus throat microphone systems have heretofore been deemed inadequate.